Conventionally, mobile communication systems capable of connecting a radio access network of 2G/3G schemes (UTRAN: Universal Terrestrial Radio Access Network or GERAN: GSM EDGE Radio Access Network), and a radio access network (E-UTRAN: Evolved Universal Terrestrial Radio Access Network) of an LTE (Long Term Evolution) scheme have been known.
An “SRVCC (Single Radio Voice Call Continuity) scheme” is specified in TS23.216 of the 3GPP (see Non-Patent Document 1). In the SRVCC scheme, a path is switched from a path via the E-UTRAN/UTRAN (path for VoIP (Voice over IP) communication) to a path via the UTRAN/GERAN (path for CS (Circuit Switch) communication) without disconnection of a path for voice call between UE (User Equipment) #1 and UE#2.
Furthermore, a “vSRVCC (Single Radio Video Call Continuity) scheme” is standardized by TR23.886 of the 3GPP (see Non-Patent Document 2). In the vSRVCC scheme, a path is switched from a path via the E-UTRAN/UTRAN (path for VoIP communication) to a path via the UTRAN (path for CS communication) without disconnection of a path for video call between UE#1 and UE#2.